Osteoarthritis (OA) is the most common degenerative disease of the human articular cartilage. OA causes pain and deformity of the articular joint, leading to significant functional deficiencies in daily life. OA occurs in the weight-bearing joints of the hips, spine, and most commonly, the knees. Many adults with OA have arthritis-attributable activity limitations, and they have a significantly worse quality of life than those without arthritis. Medical cost is another OA-related issue. The number of adults with arthritis continues to rise, resulting in growing numbers of total knee arthroplasty (TKA) procedures. Due to the increasing burden of treatment for OA, there is a need for low cost, high impact treatment alternatives.
In western countries, OA symptoms are more prevalent in the medial compartment of the knee than in the lateral compartment. The external knee adduction moment (KAM) has been developed for understanding the mechanical etiology of medial compartment knee OA. In the stance phase, the first peak of the KAM occurs during early stance, while the second peak occurs during late stance. The KAM is considered a surrogate measure for the medial tibiofemoral contact force and is widely used to quantify the load reducing effect of therapeutic intervention from devices such as wedged insoles and knee braces. In vivo analyses with instrumented knee prostheses have revealed a strong correlation between medial compartment loading and the KAM. The first peak of the KAM during walking has been linked with the presence of pain and severity of medial compartment knee OA. Reducing this peak can alleviate the pain while preventing further development of OA. Therefore, there is a need for devices that can reduce the first peak of the KAM as a therapeutic target.
The standard treatments for symptomatic knee OA are pharmacological treatments including nonsteroidal anti-inflammatory drugs (NSAIDs) or Tramadol, rehabilitation for cases of mild OA, orthoses, and partial or total knee replacement for severe OA. Other options include injection-based biomaterials, disease-modifying OA drugs, and regenerative therapy, but these options can be challenging. Despite the fact that OA patients are mostly over sixty years old, the healing potential linked to regenerative therapy decreases for patients older than sixty. The most effective method for treating OA in elderly people is TKA, which corrects the bone alignment in order to modify the mechanical loading and kinematics in the knee. Although most patients are relieved of pain, some feel dissatisfied with TKA. There is no strong evidence for the effectiveness of treatment between NSAIDs/rehabilitation and TKA in the mild OA population. Rehabilitation can be an effective therapeutic approach, but regarding the mechanism, the benefits of physical therapy may not be correlated with the reduction of the KAM, which indicates that rehabilitation may be inadequate to slow OA development.
On the other hand, orthotic knee braces have been developed and designed for reducing the load on the knee, and can be effective in reducing pain. However, braces can be inadequate for reducing the load while standing, or reducing biomechanical alterations while walking. Further, after continual use, muscle weakness can begin to occur. Therefore, there is a need for an orthosis that can reduce the loading of the knee without damaging the muscle surrounding the knee, not only during passive use (i.e. sitting), but also during active use (i.e. standing and walking).